1. Field of the Invention
The present invention relates to a liquid crystal display and a manufacturing method therefor, and particularly to a liquid crystal display having a reflector and a transparent regions in one pixel and a manufacturing method therefor.
2. Description of Related Art
At the moment a transflective liquid crystal display having a reflector and a transparent regions in one pixel is suggested. In a bright place, the transflective liquid crystal display uses surrounding outside light as a light source. Specifically, the surrounding outside light is reflected by the reflector region that is provided in a pixel to a visible side in order to display. In a dark place, the transflective liquid crystal display mainly uses backlight or the like provided to the backside thereof as a light source. Specifically, light from the backlight passes through to the visible side in the transparent region provided in a pixel. As described in the foregoing, the transflective liquid crystal display is able to display using both the light from the backside light source and surrounding light from outside. This enables to display with high visibility under any kind of surrounding light. Accordingly transflective liquid crystal displays are coming into practice mainly as displays for cellular phones that are used not only inside but also outside.
By the way, many of the transflective liquid crystal displays currently used practically employ ECB (Electrically Controlled Birefringence) that drives homogeneous aligned liquid crystal cells by vertical electric field. On the other hand, transmissive liquid crystal displays employ a wide viewing angle mode such as IPS (In Plane Switching) and VA (Vertical Alignment). Accordingly transflective liquid crystal displays have a problem of narrower field of view as compared to IPS and VA that are widely used as transmissive liquid crystal displays for liquid crystal monitors and liquid crystal display televisions.
Therefore a technique to achieve a wide viewing angle in a transflective liquid crystal display is disclosed in Japanese Unexamined Patent Application Publication No. 2003-344837 and Japanese Unexamined Patent Application Publication No. 2005-106967. In these documents, IPS, one of the display modes of horizontal electric field drive system achieving a wide viewing angle, is used. Further, as a drive system other than IPS system, a liquid crystal display using FFS (Fringe Field Switching) is also disclosed.
In Japanese Unexamined Patent Application Publication No. 2003-344837, comb-like pixel electrodes and common electrodes disposed alternately are formed to drive liquid crystal by horizontal electric field. Further, a reflector plate is placed under a part of the pixel and common electrodes with an insulating film interposed therebetween. The region having the reflector plate placed thereon is referred to as a reflector region, while the region not having the reflector plate placed thereon is referred to as a transparent region. Accordingly in the reflector region, light controlled by horizontal electric field driven liquid crystal is reflected by the reflector plate and output to the visible side. On the other hand, in the transparent region, light from the backlight is controlled by horizontal electric field driven liquid crystal and output to the visible side.
In Japanese Unexamined Patent Application Publication No. 2005-106967, comb-like pixel electrodes and common electrodes disposed alternately are formed to drive liquid crystal by horizontal electric field. Further, the pixel and common electrodes are formed of metallic materials that reflect light. Accordingly in a reflective display, light controlled by liquid crystal molecules on the pixel electrode is used. In a transparent display as in a conventional technique, light controlled by horizontal electric field between the comb-like electrodes is used.
The principle of operation for FFS mode used in IDW/AD' 05 (LCTp1-3 and p103-106) is briefly described hereinafter. Generally in FFS mode, a pixel electrode is placed above a common electrode. An insulating film is placed between the common and pixel electrodes. Further, the pixel electrodes are processed in slits. A fringe electric field in oblique direction is generated between an edge portion of the slit side of the pixel electrode and the common electrode. Liquid crystal molecules are driven using the fringe electric field so as to display. In the technique disclosed in IDW/AD' 05 (LCTp1-3 and p103-106), a part of the common electrode is formed of a transparent conductive film, while the remaining is formed of a reflective conductive film. This realizes a transflective liquid crystal display having a reflector and a transparent regions in one pixel.
However in the transflective liquid crystal displays disclosed in IDW/AD' 05 (LCTp1-3 and p103-106), there are following problems. For example in the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2003-344837, the reflector plate is generally formed by Al alloy with high reflectivity. Therefore, there is a problem that the reflector plate brings a bad influence between comb-like pixel and common electrodes. Specifically, liquid crystal driving electric field between comb electrodes is influenced by the reflector plate that is placed in a lower layer. Thus it is difficult to control the liquid crystal molecules in the reflector region, thereby making it difficult to achieve a favorable display quality.
In the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2005-106967, comb electrodes are used as a reflector region. On the comb electrodes, it is hard for liquid crystal molecules to move by the electric field between the comb electrodes. Accordingly to achieve a favorable reflective characteristic, the comb electrode must be processed three-dimensionally. Thus more processes are required and difficult technique is required. Further, the number of processes for manufacturing increase, thereby lowering productivity.
In the configuration disclosed in IDW/AD' 05 (LCTp1-3 and p103-106), a transparent region is formed in a pixel. Thus it is required to form two layers of common and pixel electrodes with a transparent conductive film. Moreover, to form a reflector region in a pixel, a reflector plate must be added to a part of the common electrode. Therefore, the number of manufacturing processes is increased as compared to an array manufacturing process of a common transflective liquid crystal display. Thus the productivity is reduced. As described in the foregoing, in a conventional liquid crystal display, there is a problem that it is difficult to accomplish a liquid crystal display having a favorable display quality.